The present invention relates to the field of valves for controlling the flow of fluids therethrough, and more particularly to the field of ball valves. More particularly still, the present invention relates to a cam-actuated split ball valve resulting in low operating torque over a wide range of operating pressures.
In the past, many popular types of valves have been used in many and various environments and applications to control the flow of fluids through a pipeline, conduit, or the like. Gate valves, plug valves, wedge valves, and ball valves, for example, have all found their respective niches in the art of fluid flow control. It is of primary importance for such valves to provide for substantially leak-free operation; it is especially so for valves regulating the flow of high pressure fluids, or potentially hazardous fluids such as highly flammable or caustic substances. Ease of operation, that is, opening and closing, is sometimes as important a feature of a valve, particularly a high pressure valve, as leak-free operation. If a valve cannot be operated quickly and with relatively little effort, besides the wear and tear on the valve parts, the excess time and effort spent in operating the valve, and the related inconvenience associated with such a stubborn valve, it can also lead to other adverse consequences, even posing a threat to lives or property. For example, if a fire were to occur in the vicinity, safety measures taken in precious seconds could mean the difference between containing the emergency, and courting all-out disaster. A valve left open momentarily because the operator could not close it quickly enough could feed the fire, or worse yet, could cause or contribute to an explosion or the like.
Thus, it is clearly desirable and advantageous to employ valves that are both reliable, that is, leakproof, and fast and easy to operate, preferably requiring very low torque attainable with only hand or light tool application. Various approaches have been taken in the past toward meeting these two objectives, with varying degrees of success. For example, floating ball valves have typically employed some means of forcing the seats against the ball mechanically during assembly of the valve in order to seal effectively at low pressures. This practice results in very high operating torque, which is undesirable for the reasons mentioned above. In order to avoid these problems, some manufacturers have chosen to forego low pressure sealability altogether to maintain a reasonably low operating torque. For some types of gate valves, a split gate is employed which relies upon a wedging action of one gate member against the other to force the gate members apart and into sealing engagement with the seats. Such a wedging action itself often requires high input or operating torque, since usually the gate members are spring biased together, and one gate member must be dragged over the other against this spring to force the members apart.
One approach used in the past to reduce the operating torque requirements of valves has been to use shifting seal members, such as shifting O-rings, to eliminate the upstream seal and to limit the formation of a seal to the downstream side of the valve. Such shifting O-rings have been used, for example, in prior art gate valves and plug valves. An example of a shifting O-ring in a gate valve is found in U.S. Pat. No. 2,861,771, issued Nov. 25, 1958, to Bryant. U.S. Pat. No. 2,950,897, issued Aug. 30, 1960, to Bryant discloses additional examples of the use of shiftable O-rings in both a gate valve and a plug valve to effect various desired upstream and downstream seal configurations to accommodate various operating conditions. U.S. Pat. No. 3,307,826, issued Mar. 7, 1967, to Lowrey discloses a through conduit slab gate valve which includes shiftable O-rings employed in pressure actuated seat members. Rather than sealing on one side only of the gate, however, the pressure actuated seat members of Lowrey utilize line pressure to provide an effective seal on both the upstream and downstream sides of the gate. Reliance on shifting O-ring seals is at times undesirable, however, because the O-rings can wear or deteriorate, becoming inoperative and thus defeating their purpose; if they leak, the result (e.g., a valve which is very difficult to open) can be as inconvenient or as undesirable as leakage of the primary valve seals in the first place. In addition, manufacture of valves using shifting O-rings or the like is relatively expensive and complicated, because the bodies have to be provided with shaped seal ring cavities to accommodate the shifting of the seals, and also channels or passages to convey line and body cavity pressures to the desired locations.
Another approach used in the past in connection with floating ball valves toward improving full pressure range sealability while attempting to keep operating torques low has been to spring-bias the seats against the ball closure member, and to change the manner of sealing engagement against the ball under varying applied loads. For example, U.S. Pat. No. 3,331,581, issued Jul. 18, 1967, to O'Connor discloses spring-seat sealing for ball valves using relatively soft plastic seat rings which are biased into engagement with the closure ball and engage the ball to a greater or lesser extent as the applied load varies. Another example of such an approach is found in U.S. Pat. No. 2,989,990, issued Jun. 27, 1961, to Bass, et al. wherein a pair of seat seals of nylon or the like are biased into sealing engagement with the ball by torsional force, and the degree of engagement between the seats and ball varies as applied pressure varies. Valves of these types which rely on the spring biasing ability of plastic seats to maintain full pressure range sealability are susceptible of seal failure due to loss of elastic memory of the seat materials, leading to loss of the spring biasing effect; deterioration of the seats due to exposure to harsh or corrosive line fluids; or to physical damage to delicate "spring fingers" created by the flexible seats.
In addition to valves of the foregoing types, trunnion-mounted ball valves have also been employed in the past to control fluid flow. In such a valve, the solid closure ball is not free to float in the valve cavity, but rather is restrained at both an upper and a diametrically opposed lower location against upstream or downstream movement of the ball. Such valves may be provided with spring biased seats, but are not provided with any means of forcing the solid ball mechanically against the seats, due to the intended restraining action of the trunnion mounting. Thus, they are also susceptible of seal failure for the same reasons mentioned previously for floating ball valves relying on plastic spring biased seats.
It is an object of the present invention to overcome the problems discussed above by providing a valve which will seal effectively over the full operating range, but yet can be operated quickly, easily, and with a minimum of torque. It is also an object of the present invention to provide such a valve which is reliable, durable, and relatively inexpensive to manufacture. It is also an object of the present invention to provide such a valve which retains its ease of operation and low operating torque at very high working pressures.